Formation of the Hawaiian Island Chain
The vast majority of earthquakes and volcanic eruptions occur near plate boundaries, but there are some exceptions. For example, the Hawaiian Islands, which are entirely of volcanic origin, have formed in the middle of the Pacific Ocean more than 3,200 km from the nearest plate boundary. How do the Hawaiian Islands and other volcanoes that form in the interior of plates fit into the plate-tectonics picture?Plate Tectonics and the Hotspot Theory
According to the plate tectonics theory, the Earth's surface consists of about a dozen rigid slabs or plates, each averaging at least 50 miles thick. These plates move relative to one another at average speeds of a few inches per year. The great majority of the world's earthquakes and active volcanoes occur near the boundaries of the Earth's shifting plates. Why then are the Hawaiian volcanoes located near the middle of the Pacific Plate more than 2,000 miles from the nearest plate boundary?J. Tuzo Wilson came up with the Hotspot Theory in 1963. According to his theory, the Hawaiian Island chain resulted from the Pacific Plate moving over a deep, stationary hotspot in the mantle, located beneath the present-day position of the Island of Hawaii. Heat from this hotspot produced a persistent source of magma by partly melting the overriding Pacific Plate. The magma then rises through the mantle and crust to erupt onto the seafloor, forming an active seamount. Over time, countless eruptions cause the seamount to grow until it finally emerges above sea level to form an island volcano. As the plate movement carries the island beyond the hotspot, the magma source is cutoff, and volcanism ceases. As one island becomes extinct another develops over the hotspot. This trail of volcanic islands and seamounts can be seen across the Pacific Ocean floor.
Artist's conception of the movement of the Pacific Plate over the
fixed Hawaiian "Hot Spot," illustrating the formation of the Hawaiian
Ridge-Emperor Seamount Chain. (Source: Maurice Krafft, Centre de
Volcanologie, France).
TopAccording to Wilson's hotspot theory, the volcanoes of the Hawaiian chain should get progressively older and become more eroded the farther they travel beyond the hotspot. The oldest volcanic rocks are on Kauai (northwesternmost inhabited Hawaiian island). The youngest volcanic rocks are found on the island of Hawaii, which is the southeastern most island in the Hawaiian Island chain. This is true because of the volcanic activity now taking place. Part of the Big Island, the southeasternmost and youngest island, presently overlies the hot spot and still taps the magma source to feed its two currently active volcanoes, Kilauea and Mauna Loa. The active submarine volcano Loihi, off the Big Island's south coast, may mark the beginning of the zone of magma formation at the southeastern edge of the hot spot. The other Hawaiian islands that have moved northwestward beyond the hot spot were successively cut off from the sustaining magma source and are no longer volcanically active. Progressive, northwesterly drift of the islands from their point of origin over the hot spot is well shown by the ages of the principal lava flows on the various Hawaiian Islands from northwest (oldest) to southeast (youngest), given in millions of years: Kauai, 5.6 to 3.8; Oahu, 3.4 to 2.2; Molokai, 1.8 to 1.3; Maui, 1.3 to 0.8; and Hawaii, less than 0.7 and still growing.
Space Shuttle photograph of the Hawaiian Islands, the southernmost part
of the long volcanic trai of the "Hawaiian hotspot". Kauai is
in the lower right corner (edge) and the Big Island of Hawaii in the
upper left corner. Note the curvature of the Earth (top edge).
(Source: NASA.)
Even on the Big Island alone, the relative ages of its five volcanoes are compatible with the hot-spot theory. Kohala, at the northwestern corner of the island, is the oldest, having ceased eruptive activity about 60,000 years ago. The second oldest is Mauna Kea, which last erupted about 3,000 years ago; next is Hualalai, which has had only one historic eruption (1800-1801), and lastly, both Mauna Loa and Kilauea have been vigorously and repeatedly active in historic times. Because it is growing on the southeastern flank of Mauna Loa, Kilauea is believed to be younger than its huge neighbor.
If the hot-spot theory is correct, the next volcano in the Hawaiian chain should form east or south of the big Island. Abundant evidence indicates that such a new volcano exists at Loihi, a seamount (or submarine peak) located about 20 miles off the south coast of the Big Island. Loihi rises 10,100 feet above the ocean floor to within 3,100 feet of the water surface. Recent detailed mapping shows Loihi to be similar in form to Kilauea and Mauna Loa. Its relatively flat summit apparently contains a caldera about 3 miles across; two distinct ridges radiating from the summit are probably rift zones.
Map of part of the Pacific basin showing the volcanic trail of the
Hawaiian hotspot - 6,000-km-long Hawaiian Ridge-Emperor Seamounts chain.
(Source: World Ocean Floor by Bruce C. Heezen and Marie Tharp,
Copyright 1977.)
Active and Potentially Active Volcanoes in Hawaii
| Volcano | Eruption type(s) | Number of eruptions in past 200 Years | Latest activity (in years before present or year(s) A.D.) | Remarks |
| Haleakala | Lava, ash | 1 | 1790 | In last stage of Hawaiian volcanic cycle. Expected recurrence rate estimated to be about 200-600 years. |
| Hualalai | Lava, ash | 1 | 1800-01 | High hazard due to unusually fluid lava. |
| Kilauea | Lava, most common; ash, rare | 47 | On going from 1983 | Explosive eruption at Kilauea summit in 1790 killed approximately 80 Hawaiian warriors. Eruptions presenting lava-flow hazard to coastal areas: 4 in the 19th century; 5 in the 20th century. |
| Kohala | Lava, ash | 0 | 120,000 years ago | Volcanic cycle may not be completed, but eruption probability is low. |
| Loihi | Lava | Not known | Not known | Submarine volcano; seismically active; youngest lava less than 1,000 years old. |
| Mauna Kea | Lava, ash | 0 | 4,000 years ago | Frequency of activity before latest eruption is estimated to be about 300 years. |
| Mauna Loa | Lava | 30 | 1984 | Eruptions presenting lava-flow hazard to coastal areas: 8 in the 19th century; 8 in the 20th century. |
Volcano